Electron tube



A. LIEB ELECTRON TUBE Feb. 21, 1956 2 Sheets-Sheet 1 5 Filed Jan. 26, 1954 INVENTOR A. uasgflfi F ATTORNEY l O/ O O O Fig. 3

Feb. 21, 1956 A. LIEB 2,735,955

' ELECTRON TUBE Filed Jan. 26, 1954 2 Sheets-Sheet 2 f Fig. 6A Fig. 6B

AT TOR NEY United States Patent .national Standard Electric Corporation, New York,

N. Y., a corporation of Delaware Application January 26, 1954, Serial No. 406,243 Claims priority, application Germany January 29, 1953 1 Claim. (Cl. 313-494) The invention deals with electron tubes of the kind in which, grids are spaced at different distances from the cathode, and in which discharge current, flowing to one of these grids or to a number of them, introduces diffi culties and impairs the desired operation. For instance, such difficulties can occur in the case of final power-tubes, in which the electronic stream, passing into the screen grid, must as far as possible be kept small in order to secure maximum power delivery and safety of service.

In addition to the-customary amplifier pentodes there are discharge systems, designated as beam power-systems, in which the turns of the control grid and those of the screen grid are of the same pitch and so positioned as to be level with each other. With the grids so arranged, disc-shaped bundles of electrons will form between the turns thereof, whereby the amount of current flowing into the screen grid shall be relatively small. This amount will be smaller the sharper the electrons from the cathode are focussed by electron optics and thus introduced into the interspaces between the screen grid turns, such electron optics being composed of the control grid and the cathode. Obviously the focussing will be best as soon as a sharp focal point or crossover has been produced and if this point is situated, at least approximately, in the spatial face or plane of the screen grid wires. This requirement can be fulfilled where the throughgrip of the screen grid (the reciprocal of the amplification factor thereof). is relatively great. But the said requirement is impossible to fulfill if the throughgrip is of such small values as is desirable particularly in powerful tubes of high anode-current slope, for in this case the focal point either falls within the spatial face or plane determined by the control grid wires, or will be located in close proximity to that face.

The invention therefore provides that the screen grid and the control grid be so constructed and arranged that the electrons from the cathode shall be focussed by neighboring interstices of the control grid, at least by two such interstices, and thus be introduced into one screen grid interstice allocated to these. By this means the amount of current taken up by the screen grid will be small despite a small throughgrip of the screen grid. In order to accomplish such focussing, turns of that grid which is nearest to the cathode may be made thicker than other turns of this grid, or some turns of said grid may be spaced from the cathode at distances different from those at which other turns thereof are spaced from the cathode.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood, by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

Fig. 1A is a sectional view of a portion of a tube showing the grid structures;

2,735,955 Patented Feb. 21, 1956 ice Fig. 1B is an elevational view of the structure of Fig. 1A;

Figs. 2, 3, 4, 5 and 6A are sectional views of modifications of the structure shown in Fig. 1B, and

Fig. 6B is an elevational view of Fig. 6A.

Fig. 1B shows diagrammatically a sectional View 1A and an elevation of one embodiment of the invention as employed in a final power-tube. The cathode 1 is surrounded by the control grid 2 and the screen grid 3. Grid 2 is composed of two wire helices 2a, 2b. The wire of helix 2a is thicker than that of 2b. Screen grid 3 is a wire helix of the same pitch as grid 2. The turns of grid 3 are level with those of helix 20.

Fig. 2 represents a slight modification of what is shown in Fig. 1A. The control grid according to Fig. 2 comprises three helices 2a, 2b, 2c. The turns of these are spaced from each other differently. Screen grid 3 is again of the same pitch as grid 2. The turns of grid 3 are level with those of the helices 2a, 2b.

The embodiment represented in Fig. 3 diflers from that in Fig. 2 in respect of the distance between the turns of the helices 2a, 2!), this distance being somewhat larger in Fig. 3 than it is in Fig. 2. By dimensioning this distance appropriately the amount of current taken up by screen grid 3 will be particularly small.

Still another embodiment is represented in Fig. 4. Here the control grid 2 is composed of two helices 2a, 2b of which the helix 2a is larger in diameter than 21;. The turns of screen grid 3 are level with those of the helix 2a.

In the embodiment illustrated in Fig. 5 the control grid comprises three helices 2a, 2b, 2c. The turns of the helices 2a, 20 are level with each other, helix 2c being larger in diameter than 2a. The pitch of screen grid 3 is the same as that of the control grid. The turns of grid 3 are level with those of the helices 2a, 2c.

An embodiment different from the others here described is represented in Fig. 6B. In the case of Fig. 6 the control grid 2 is constituted by only one helix 2a. Certain halfturns of this helix are in a periodical succession spaced at a larger distance from the cathode 1 than are the other turns or half-turns. The various distances of spaces of the individual or half-turns of the grid from the cathode can be attained e. g. by stretching or profiling performed with the aid of a suitable expanding mandrel that is provided with differently deep recesses adapted to the different interspacings between the individual turns. It is also possible to arrange the turns of that grid which is closer to the cathode, and the turns of that grid which is farther away from the cathode, on two grid supporting rods each and to combine or to arrange these turns in a suitable manner. Furthermore it is possible to arrange the turns of the grid, which is farther away from the cathode, on the outside of the supporting rods and the turns of the grid, which is closer to the cathode, on the inside of the grid supporting rods. Moreover the pitch of the screen grid 3 is a multiple of that of the control grid 2. In the example here shown the pitch of grid 3 is three times that of grid 2. The turns of grid 3 are level with those half-turns whose distance from the cathode is, as stated, larger than that of the other half-turns. In order that such leveling may be practicable to the highest possible perfection, the outer diameters of the two grids are in the ratio 1:3. The invention also contemplates combinations of the arrangements here described. For example, by combining the principle underlying Figs. 1A and 4 a discharge device can be constructed in which the current taken up by the screen grid will be particularly small.

It will be obvious to all those skilled in the art that the grid arrangement here disclosed is applicable not alone to final power-tubes but to other discharge systems 8 in which it will be advantageous that the current taken up by one or more grids is small.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claim.

What is claimed is:

An electron discharge device comprising a cathode and a plurality of grids surrounding said cathode at diffcrcnt distances therefrom, comprising a first grid having interstices between successive turns at least two of which fit within the interstice between two successive turns of a References Cited in the file of this patent UNITED STATES PATENTS 2,038,360 Harries Apr. 21, 1936 2,167,826 Bull Aug. 1, 1939 2,195,079 Deroche Mar. 26, 1940 2,501,002 Parker Mar. 21, 1950 -a in 

